My optical drive had failed long ago and after having already updated my HD to an SSD I had found the space to be lacking. My fan has also sounded like a baseball card in bicycle spoke for the last couple of years, it was often so loud that I could not leave this machine running and sleep in the same room.
I felt like whatever guide I followed was a bit lacking. There is a screw in the regular HD bay hidden behind some rubber codding that holds the optical drive down. There is also a wire running along the optical drive enclosure that is held down with some tiny clips. I had to carefully work it free and with the drive bay in place it now floats freely in there.
The new fan is completely silent. After reassembly I was concerned because I didn't have any felt tape to secure the fan to the rear vent nor did I bother to tape it down with anything else. But the results were evident after a bit of uptime. This was well worth $50 bucks.
The first time I took my Macbook apart I lost some screws and poorly seated some that I managed to retain because I lacked proper tools. I was in Afghanistan. This time I ordered a spudger because removing the upper case is the most tricky portion of this task. I have the cracks in the edges of my case to prove it. This machine will continue to be a super stable workhorse in my collection well beyond a decade of use. This is not an upgrade for the clumsy or disorganized, nor is it as simple as the install video seems to portray, but it is worth the trouble and cash.
9.5 mm PATA Optical Bay SATA Hard Drive Enclosure